Eli5 How does the bike pump measure the PSI?

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So my bike’s wheels say something like 40PSI, and when I feel the wheel is kinda deflated or not fully inflated, I use the bike pump and pump until the gauge indicates 40PSI, but since the gauge starts at 0, and there was already some air left in the wheel, does that mean I went over 40PSI? Or does the bike pump compensates for the leftover air somehow? How should I properly pump the wheels to the recomended PSI?

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Anonymous 0 Comments

The gauge didn’t start at zero if the tire is only kinda deflated. There is pressure in there when you start pumping. Pop the gauge on there next time it feels a bit flat, before you pump. You’ll see the pressure of the air currently in the tire. You are pumping additional air to reach a final pressure of 40 psig.

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